This paper proposes a method to design low-density parity-check (LDPC) codes for delayed bit-interleaved coded modulation (DBICM). In the method, the code variable node (VN) degree distributions and the assignments of VNs with different degrees to DBICM subchannels are optimized via two cascaded differential evolution (DE) steps. In each step, to optimize VN degree distribution or channel assignment, a parity-check matrix is constructed, and the associated decoding threshold is calculated for each element in a generation. In constructing a parity-check matrix for each channel assignment, we propose a constraint PEGlike code construction method. Protograph-EXIT is employed to calculate the decoding threshold for each parity-check matrix. We apply the proposed method to construct irregular binary LDPC codes for both 16-QAM DBICM and BICM schemes. Simulation results demonstrate that the optimized LDPC codes are within 1 dB from the associated capacity limit at a bit error rate (BER) of 10-6. Besides, the LDPC coded DBICM achieves an SNR gain of 0.5 dB to 0.1 dB over BICM counterparts at a code rate ranges from 0.25 to 0.5.

In this paper, a method to perform parallel decoding of the errors within a burst is presented for cyclic codes. It is shown that O(L) operations per position are sufficient to estimate each error of a burst of length L in parallel.

We introduce a new class of low-rate error correction codes called concatenated zigzag Hadamard (ZH) codes which are specified by a highly structured zigzag graph with each segment being a Hadamard codeword. The ZH codes enjoy extremely simple encoding and very-low-complexity soft-input soft-output (SISO) decoding. We present an asymptotic performance analysis of the proposed codes using the extrinsic mutual information transfer (EXIT) chart for infinite-length codes. We also provide a union bound analysis of the error performance for finite-length codes.

In this correspondence, we introduce a new class of low-rate error correction codes called zigzag Hadamard (ZH) codes and their concatenation schemes. Each member of this class of codes is specified by a highly structured zigzag graph with each segment being a Hadamard codeword. The ZH codes enjoy extremely simple encoding and very low-complexity soft-input-soft-output (SISO) decoding based on a posteriori probability (APP) fast Hadamard transform (FHT) technique. We present an asymptotic performance analysis of the proposed concatenated ZH codes using the extrinsic mutual information transfer (EXIT) chart for infinite-length codes. We also provide a union bound analysis of the error performance for finite-length codes. Furthermore, the concatenated ZH codes are shown to be a good class of codes in the low-rate region. Specifically, a rate-0.0107 concatenated code with three ZH components and an interleaver size of 65536 can achieve the bit error rate (BER) performance of 10/sup -5/ at -1.15dB, which is only 0.44 dB away from the ultimate Shannon limit. The proposed concatenated ZH codes offer similar performance as another class of low-rate codes-the turbo-Hadamard codes, and better performance than superorthogonal turbo codes, with much lower encoding and decoding complexities.

This paper provides a comprehensive study of interleave-division multiple-access (IDMA) systems. The IDMA receiver principles for different modulation and channel conditions are outlined. A semi-analytical technique is developed based on the density evolution technique to estimate the bit-error-rate (BER) of the system. It provides a fast and relatively accurate method to predict the performance of the IDMA scheme. With simple convolutional/repetition codes, overall throughputs of 3 bits/chip with one receive antenna and 6 bits/chip with two receive antennas are observed for IDMA systems involving as many as about 100 users.

We study a multi-layer space-time code, based on random interleaving and proper power allocation. We show that, theoretically, the proposed code can achieve capacity for any transmission rate by superimposing many ideal low-rate codes. We also show that, with practically available codes, the proposed scheme can achieve performance close to the theoretical limit.

This work provides a comprehensive study of IDMA systems. We first outline the basic IDMA principles in single-path and multi-path environments. We then describe a simple semi-analytical technique to assess the performance of IDMA systems, based on which we develop a power allocation scheme for performance optimization. We also discuss the use of low-rate codes to further enhance the power efficiency of IDMA systems. Simulation results demonstrate the advantages of the IDMA scheme in terms of both bandwidth and power efficiencies. For example, with simple convolutional/repetition codes an overall throughput of 8 bits/chip is achieved in single antenna systems. With turbo-Hadamard codes, performance at 1.4 dB away from the theoretical limit is demonstrated in a Gaussian MAC.

This paper presents a family of space-time codes employing interleavers to separate signals form different antennas. Noticeable performance improvement has been observed compared with existing schemes. An interactive detection algorithm is derived. The complexity involved is very low, and increases only linearly with the number of transmit antennas.

This paper presents an asynchronous interleave-division multiple-access (IDMA) scheme, in which users are distinguished by different chip-level interleaving methods instead of by different signatures as in a conventional code-division multiple -access (CDMA) scheme. A very low-cost iterative detection algorithm is derived for the IDMA scheme based on a chip-by-chip detection principle. The proposed scheme can achieve nearly optimal performance for systems with a large number of users. Furthermore, receiver simplicity as well as high performance can be maintained in multipath environments.

This paper is concerned with a class of low-rate codes constructed from Hadamard code arrays. A recursive encoding principle is employed to introduce an interleaving gain. Very simple trellis codes with only two or four states are sufficient for this purpose, and the decoding cost involved in the trellis part is typically negligible. Both simulation and analytical results are provided to demonstrate the advantages of the proposed scheme. The proposed scheme is of theoretical interest as it can achieve performance of BER=10/sup -5/ at E/sub b//N/sub 0//spl ap/-1.2dB (only about 0.4 dB away from the ultimate low-rate Shannon limit) with an information block size of 65534. To the authors' knowledge, this is the best result achieved to date with respect to the ultimate Shannon limit. With regard to practical issues, the decoding complexity of the proposed code is considerably lower than that of existing low-rate turbo-type codes with comparable performance.

Techniques using interleaving as the basic means for signal separation are introduced for both multiple access systems and multiple transmit antenna systems. A very low-cost chip-by-chip iterative detection algorithm is presented. The proposed schemes can achieve nearly optimal performance for system with a large numbers of users or transmit antennas.